| context | $X $ |
| definiendum | $ \langle\!\langle X,\Sigma,\mu \rangle\!\rangle$ in it |
| postulate | $ \Sigma \in \mathrm{SigmaAlgebra}(X) $ |
| postulate | $ \mu\in \mathrm{Measure}(\Sigma) $ |
A measure space is a measurable space together with a fixed measure.
Wikipedia: Measure